1. Field of the Invention
The present invention relates to wireless communications and, more particularly, to wireless signal repeaters. Such repeaters can be usefully employed to enhance wireless communications of various types. For purposes of example, this description will focus mainly on cellular wireless communications, such as CDMA communications for instance.
2. Description of Related Art
Cellular wireless is an increasingly popular means of personal communication in the modern world. People are using cellular wireless networks for the exchange of voice and data over cellular telephones, personal digital assistants (PDAs), cellular telephone modems, and other devices. In principle, a user can seek information over the Internet or call anyone over a public switched telephone network (PSTN) from any place inside the coverage area of the cellular wireless network.
In a typical cellular wireless system, an area is divided geographically into a number of cell sites, each defined by a radio frequency (RF) radiation pattern from a respective base transceiver station (BTS) antenna. The base station antennae in the cells are in turn coupled to a base station controller (BSC), which is then coupled to a telecommunications switch (e.g., mobile switching center (MSC)) or gateway (e.g., packet data serving node (PDSN)) that provides connectivity with a transport network such as the PSTN or the Internet.
When a mobile station (such as a cellular telephone, pager, or appropriately equipped portable computer, for instance) (MS) is positioned in a cell, the MS and BTS can communicate with each other in various channels over the RF air interface. Communications from the BTS to an MS are considered to be in a “forward” direction, so the air interface channels used to carry such communications are referred to as the “forward link” channels. Conversely, communications from an MS to the BTS are considered to be in a “reverse” direction, so the air interface channels used to carry such communications are referred to as “reverse link” channels.
With the continued growth in popularity of wireless communications, people are increasingly engaging in cellular wireless communications in place of traditional landline communications. This is of course most notable within buildings, such as homes and offices, where landline communications, such as traditional telephone and computer networks, were once the only method available. Use of mobile stations instead of fixed landline terminals conveniently allows for free movement within such buildings as well as into and out of the buildings.
Unfortunately, however, cellular wireless communications can suffer from varying levels of signal degradation as signals are carried over the air interface between the mobile station and the base station. Most significantly, for instance, the strength of signals transmitted in the forward link direction from the base station to the mobile station can diminish substantially as the signals travel over increased distance to the mobile station. Further, obstructions such as buildings and foliage can attenuate or otherwise degrade signals passing over the air interface.
When a mobile station operates within a building, the problem can be even more acute, as the structure of the building can further diminish the signal. In a worst case scenario, forward link signals that ultimately arrive at a mobile station within a building may be too weak to be detected and/or used by the mobile station. As a result, service could be unavailable and wireless communications could be blocked or dropped. This is clearly a problem for cellular wireless carriers who are seeking to promote in-building use of their service.
One approach that can be used to overcome this difficulty is to increase the power transmitted by the base station. A disadvantage with this approach, however, is that the increased power can lead to increased interference in adjacent cells. This, in turn, can decrease the capacity of the wireless network. The power increase can also interfere with other wireless devices in use around the base station. The magnitude of the power increase proportionally affects the amount of interference produced by the base station, with a greater power increase causing a greater interference.
Also, this approach would only solve half of the problem. Increasing the signal strength from the base station would allow a mobile unit to receive the base station's signal in areas that highly attenuate that signal. It would not aid the base station in receiving a signal from a mobile station. Cellular service is primarily a bi-directional mode of communication, in which connections are established and maintained through control signals that are sent both directions between the base station and a mobile station. Therefore, in order to support bi-directional communication, an increase in the transmission power of the base station would require a corresponding increase in the transmission power of the mobile station.
Another approach to help increase wireless signal strength within a building is to provide a distributed antenna system in the building. In this approach, a hub is connected, via wired links, to one or more wireless access points in the building. The wired link is typically a coaxial cable, a 10Base-T cable, or a fiber optic cable. The hub transmits the RF signals from the base station to the wireless access points, via the wired links. The wireless access points, in turn, transmit the RF signals into the building, where they may be received by mobile stations. Similarly, the wireless access points receive RF transmitted by the mobile stations and transmit the RF to the hub, via the wired links. The hub, in turn, transmits the RF to the base station. In this way, the wireless coverage area provided by the base station may be enhanced within the building.
A disadvantage with this latter approach, however, is that cabling is often difficult and expensive to install. This is especially true in buildings where cabling may have to be installed inside walls or in other difficult to access areas. Further, another disadvantage with this approach is its inflexibility resulting from the use of dedicated wired connections. In particular, a wired network is not easy to reconfigure, as additional cabling must be installed.